The present invention relates to a technique for introducing error resilience in video transmission over a wireless channel and, more particularly, to the utilization of a transcoder in the wireless communication path to inject resilience into video transmission over the wireless channel.
Traditional xe2x80x9cwiredxe2x80x9d communication channels for video signals have relatively high bandwidth and consistently low bit error rates. This is in stark contrast to the wireless environment, where a typical wireless channel generally exhibits a lower bandwidth and an error rate that is both greater than the wired channel and time-varyingxe2x80x94both during a given transmission as well as from one transmission to another.
The time-varying conditions of a wireless channel may, ideally, use feedback from the decoder to the encoder to adapt its coding parameters (for example, bit rate) to the time-varying conditions. However, such a solution is not practical in many situations. First, in a multicast environment (very typical of video transmission), an encoder can only produce a single bitstream, while each receiver may have different capabilities due to the characteristics of both the end terminal and the wireless channel. Additionally, in applications in which a compressed video bitstream is stored for future delivery, the encoder cannot, in real time, directly change the resilience of the bitstream. Lastly, an encoder designed for use on a xe2x80x9cwiredxe2x80x9d channel is usually not cognizant of the characteristics of any xe2x80x9cwirelessxe2x80x9d hops that may be included on the signal path. That is, an encoder will generally operate without knowledge of any wireless hops between the encoder and decoder. There is, and will continue to be, an embedded base of encoders designed to generate bitstreams optimized for reasons other than resilience in wireless channels.
Previous transcoders have been limited in their functionality to only reduce the bit rate of the video signal from the encoder, operating under the implied assumption that resilience can only be increased via channel coding, such as forward error correction (FEC) or automatic repeat request (ARQ). However, using only channel coding limits the type of resilience that can be employed and does not take advantage of source coding methods to improve the resilience. In some cases, the decoding end may not be capable of implementing channel coding methods and must rely on the source-coding methods.
Based on all of the above, therefore, a need remains in the art for a robust transcoder for use in wireless communication channels that provides improved error resilience than is possible with pure bit reduction.
The need remaining in the prior art is addressed by the present invention, which relates to a technique for introducing error resilience in video transmission over a wireless channel and, more particularly, to the utilization of a transcoder in the wireless communication path to inject resilience into video transmission over the wireless channel.
In accordance with the present invention, a transcoder is implemented that provides both spatial and temporal resilience, then uses rate distortion theory, in conjunction with the source rate, to provide an output to the decoder at the same bit rate as the original encoded signal. In particular, the transcoder of the present invention selects an appropriate resilience and compression technique based upon the spatial and temporal errors discovered in the incoming bitstream. The characteristics of the wireless channel are also factored into the analysis so that the output video bitstream matches as closely as possible the wireless transmission channel.
Other and further aspects of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.